Insulated pipe systems with moisture detecting means

ABSTRACT

An insulated pipe system such as a subterranean district heating pipe system comprising a conductor pipe surrounded by a normally dry and electrically non-conducting, but hygroscopic material in which there is enclosed elongated electric conductor elements, of which one may be the conductor pipe itself, connected to means for detecting the occurrance of an electric conductivity in the hygroscopic material due to intrusion of moisture therein, in which the conductor elements between which the conductivity should be detected are connected to an alternate voltage source and are mutually connected so as to form a complex impedance, the real part of which is constituted by the resistance between the conductor elements through the hygroscopic material, the detecting means comprising a phase comparator connected so as to compare the phase of the output signal from the alternate voltage source with the phase of the signal through the complex impedance and to actuate a detector unit in response to the phase difference between the compared signals changing beyond a predetermined value.

United States Patent Lambertsen Dec. 16, 1975 INSULATED PIPE SYSTEMS WITH MOISTURE DETECTING MEANS [57] ABSTRACT [75] Inventor: Ejvind Lambertsen, Fredericia, An insulated pipe system such as a subterranean dis- Denmark trict heating pipe system comprising a conductor pipe surrounded b a normal] dr and electrically non- [73] Asslgnee' Ms Rasmussen Denmark conducting, bit hygroscopic m aterial in which there is [22] Filed: Mar. 26, 1974 enclosed elongated electric conductor elements, of

which one may be the conductor pipe itself, con- [zl] Appl' 454952 nected to means for detecting the occurrance of an electric conductivity in the hygroscopic material due [30] Foreign Application Priority Data to intrusion of moisture therein, in which the conduc- Mar. 26, 1973 United Kingdom 14316/73 tor elhmehts between which the conductivity Should be detected are connected to an alternate voltage 52 us. c1. 317/27 R; 317/1310. 3 Source and are mutually Connected so as to form a 51 Int. c1. H02H 3/38 Complex impedance, the real P of which is Consti- 53 Field f seal-chm 3 7 27 R, 7 A, DIG 3, tuted by the resistance between the conductor ele- 317 2 2 3 0 5; 324/54, 61 R, 65 R ments through the hygroscopic material, the detecting means comprising a phase comparator connected so [56] References Cited as to compare the phase of the output signal from the UNITED STATES PATENTS alternate voltage source with the phase of the signal through the complex impedance and to actuate a de- 3,678,376 7/1972 Jaster et al 324/54 Primary ExaminerJ. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorney, Agent, or Firm-Craig & Antonelli tector unit in response to the phase difference between the compared signals changing beyond a predetermined value.

10 Claims, 2 Drawing Figures INSULATED PIPE SYSTEMS WITH MOISTURE DETECTING MEANS The present invention relates to an insulated pipe system such as a subterranean district.heating pipe system comprising a conductor pipe surrounded by a normally dry and electrically non-conducting, but hygroscopic material in which there is enclosed elongated electric conductor elements connected to means for detecting the occurranceof an electric conductivity in the hygroscopic material due to intrusion of moisture therein. z

In the copending patent application Ser. No. 21,028 there is disclosed such a detecting system comprising two parallel electric conductors extending inside the heat insulation material along each of a plurality of sections of the pipe system. These wires (of which one may be the iron pipe itself) are connected to a DC voltage source and to an electric tone generator specific for each single section of the pipe system in such a manner that the tone generators are normally operative and transmit their different output signals through a common wire back to a central control station in which selective receiver means for the different signals are mounted so as to enable the operation of all the generators to be supervised. If at a point in a given section of the pipe system water or moisture becomes present in the insulation material the DC source of the particular tone generator will be more orless short circuited, and the tone generator stops working when the voltage drops below a certain lower limit. Hereby it may be registered in the control station that the signal from the particular generator is missing andthat,.therefore, there may be a risk of corrosion on the pipe in the particular section of the system. The wet point or area may thereafter be localized by a separate measurement on the wires in the concerned section.

Practice has shown, however, that the threshold value of the feeding voltage at which the generator stops its operation is not very accurately defined, or rather though it is well defined the voltage drop due to the presence of moisture is not a well defined function of the amount of moisture, so that the voltage does not always drop as much as should be expected, probably due to a galvanic effect of the water between the wires. It is a primary purpose of this invention to provide a detector system in which the threshold value of the relative amount of moisture for producing an alarm signal is better defined and can generally be a lower value than in the said earlier system, whereby an alarm in response to an uncritical moisture contents can be avoided.

According to the invention the conductor elements between which the conductivity should be detected are connected to an alternate voltage source and are mutually connected so as to form a complex impedance, the real part of which is constituted by the resistance between the conductor elements through the hygroscopic material, the detecting means comprising a phase comparator connected so as to compare the. phase ofthe output signal from the alternate voltage source with the phase of the signal through the complex impedance and to actuate a detector unit in response to the phase difference between the compared signals changing beyond a predetermined value. The use of an AC voltage between the conductor elements eliminates the problems of the said galvanic effects, andsince there is a well defined relation between the conductivity of the hygroscopic material and the said phase difference and therewith the output from the phase comparator it is possible, therefore, to obtain the desired detection at a well defined stage of the increase of the conductivity should moisture intrude into the hygroscopic material.

In a preferred embodiment of the invention the output of the phase comparator is used for controlling an electronic switch which in its turn controls the operation of the said tone generator of each single section of the pipe system.

In the following the invention is described in more detail, by way of example, with reference to the accompanying drawing, in which:

FIG. 1 is a schematic diagram of a system according to the invention, and

FIG. 2 is a corresponding diagram of another embodiment of the system.

In FIG. 1 a length of a heat insulated pipe is shown schematically at 2. This length is shown as made of two joined pipe elements, but in practice the length considered may consist of many such elements and may constitute a section of a larger pipe system, e.g. a subterranean district heating pipe system, comprising a plurality of such sections to be individually supervised for detection of moisture intruding into the heat insulation thereof. The pipe lengths comprise an inner iron tube 4 surrounded by a cylindric layer of a heat insulating material 6, preferably consisting of polyurethane foam, this layer again being surrounded by a protective outer plastics tube 8. The tube joints are each covered by a tube casing 10 so as to be sealed towards the surroundmgs.

A non-insulated electric wire 12 extends through the insulation material 6 parallel to and spaced from the iron tube 4. At one end of the pipe length the wire 12 is connected to the iron tube 4 through a condenser 14, and at the other end of the pipe length or section the wire 12 and the tube 4 are connected to a pair of terminals 16.

Thus, the resistance between the wire 12 and the tube 4 together with the condenser 14 form a complex impedance which is accessible for measurement on the terminals 16.

Adjacent the particular section of the pipe system as well as adjacent each of the other sections of the system there is mounted a detector unit comprising an oscillator 18, a phase comparator 20, an electronic switch 22, a tone generator 24 and a transformer 26. The oscillator 18 operates at a frequency which may be the same for all the sections, e.g. 3 kHz, and its output signal is fed through a wire 28 partly to a first input terminal of the phase comparator 20 and partly to one of the impedance terminals 16. The other terminal 16 is connected to a second input terminal of the phase comparator, and the output of the comparator is fed to the switch 22. This switch, in its turn, controls the power supply to the tone generator 24, the output of which is fed to the primary of the transformer 26.

The power supply to the oscillator and the tone generator is a DC voltage taken from a continuous wire 30 extending through the insulation material of the pipe lengths 2 throughout the entire pipe system. The DC voltage is supplied to the wire 30 in a central surveying station in which the wire is also connected to a selective receiver 32 adapted to register the presence of the output signals from the different tone generators. These signals are all sent to the receiver through the wire 30 which is connected in series with the secondaries of all the transformers 26. It will be understood that the DC voltage may be supplied to the various detector units through these secondary windings of the transformers 26. Another transformer 26 is shown towards the right in FIG. 1, belonging to another pipe section 2 which is shown endwise together with its associated detector unit generally designated 34.

If the insulation material is dry the resistance between the conductors4 and 12 will be very high, and the phase difference between the two input signals to the phase comparator will be 90 due to the capacity 14. If there is a short circuit between the conductors 4 and 12 the phase difference will be zero. Of course. a small amount of moisture in the insulating material will make no harm, and the system can be considered to work under normal and permissible conditions as long as the said resistance is reasonably high, e.g. above 150 Ohms. The switch 22 is so adapted that in such normal operation it is maintained closed for power feeding the tone generator'24 which thus produces its characteristic output signal. The presence of this signal may be registered by the receiver 32 in the said central station.

The intensity of the output of the phase comparator varies with the actual phase difference between the input signals thereon, and the system is so adapted that the switch 22 is switched off when the output of the phase comparator corresponds to a drop of the said resistance beyond the desired threshold value thereof. Hereby the tone generator stops its operation, and in the central station the selective receiver 32 will indicate that the signal from that particular tone generator is missing, whereafter the corresponding section of the pipe system can be inspected or subjected to lcal measurements for localizing a possible defect.

It is deemed unnecessary at this place to describe the circuits of the detector unit in more detail, since any expert in electronic controls will be able to design even many different circuits suitable for achieving the operation here described. It will be advantageous and easily possible, also, to design the switch 22 with a so-called hysteresis function so as to obtain that the tone generator is switched off in response to the resistance in the insulating material decreasing to the critical value, whilst if orwhen the moisture disappears gradually from the insulation material and the resistance increased correspondingly the tone generator will not be switched on. again until the resistance has reached a value somewhat above the critical value. It is ensured hereby that the tone generator does not start again until the moisture really tends to disappear and not only has disappeared to a stationary degree just above the critical degree.

It should be mentioned that in the system shown, in which the imaginary part of the complex impedance is constituted by a capacity, the phase comparator will react to a break of the detector wire 12 in the same manner as to a short circuit between the conductors 4 and 14, i.e. also a wire breakdown will be automatically detected.

In subterranean district heating pipe systems the pipes will normally be mounted pairwise so as to comprise a flow pipe and areturn pipe, such a pair of pipes being shown in FIG. 2 and designated 40 and 42, respectively. These pipes constitute a single section of the pipe system to be supervised by means of a detector unit corresponding to that described above. In the detector unit the reference numerals of FIG. 1 are used for designating similar parts, but the system of FIG. 2 comprises a few modifications as follows:

The two iron pipes 4 are interconnected by a wire 44, or generally the iron pipes are grounded, and the detector wires 12 are connected in series as shown at 46. The continuous wire extending along the entire pipe system, designated 30 in FIG. 1, is substituted by one continuous wire 48 extending through all the flow pipes 40 and another continuous wire 50 extending through all the return pipes 42. The wire 48 is used solely for supplying DC power to all the detector units throughout the pipe system and the wire 50 is used solely as a signal line for feeding the outputs of all the tone generators to the selective receiver in the central control station. The tone generators are each connected to the signal line 50 by means of a so-called adaption transformer 52 whereby a good impedance matching and low losses are obtainable. The said complex impedance is inductively coupled to the detector system by means of a transformer 54. At the left hand side of this transformer an equivalent diagram of the complex impedance is shown.

Numerous other modifications will be possible within the scope of the invention. Thus it could be considered to avoid the local oscillators and derive the AC-signal to the complex impedance from an AC voltage fed to the wires 30 and 48, respectively, with an AC-DC-converter mounted in the power supply to each tone generator. Also, the tone generators 24 could possibly be used for feeding their own AC-signal to the complex impedance. Other obvious modifications would be to mount the switch in the output circuit of the tone generator and to use an additional non-insulated wire as a detector conductor instead of the tubes themselves.

The basic concept of the invention is the provision of a measuring signal indicative of the phase displacement of the AC-signal passing the complex impedance in which the variable part of the impedance is the real part thereof, and it will be appreciated that the means for registering the displacement may be constituted by any of a plurality of well known devices or systems responding to or indicating the change of the output of the phase comparator as the character of this output varies with the condition to be supervised. A'conventional phase comparator will produce an output signal consisting of superimposed square pulses corresponding to the frequency of the respective input signals, these respective pulses occurring with the same phase displacement as between the input signals, whereby the length of the combined pulses and therewith the average output voltage will be a well defined function of the phase difference between the input signals. It should be unnecessary to describe in more detail the variety of manners in which the said output voltage can be measured or supervised, e.g. for automatically producing an alarm signal in response to the voltage changing to a critical value.

In the system described, however, the use of the described tone generators as detector meansis highly advantageous, because a plurality of sections of the pipe system can be supervised from a central station in an easy manner by means of the selective receiver. It should be mentioned that in a preferred embodiment of the system the selective receiver comprises an automatic step switch operating so as to sequentially and cyclincally connect to the signal line each of a plurality of tuned circuits or active filters corresponding to the different individual frequencies of the tone generators,

and indicator means operable to respond to any filter being connected without receiving its characteristic signal.

What is claimed is:

1. An insulated pipe system such as a subterranean district heating pipe system comprising' a conductor pipe surrounded by a normally dry and electrically non-conducting, but hygroscopic material in which there is enclosed elongated electric conductor elements connected to means for detecting the occurrence of an electric conductivity in the hygroscopic material due to intrusion of moisture therein, characterized in that the conductor elements between which the conductivity should be detected are connected to an alternate voltage source and are mutually connected so as to form a complex impedance, the real part of which is constituted by the resistance between the conductor elements through the hygroscopic material, the detecting means comprising a phase comparator connected so as to compare the phase of the output signal from the alternate voltage source with the phase of the signal through the complex impedance and to actuate a detector unit in response to the phase difference between the compared signals changing beyond a predetermined value.

2. A pipe system according to claim 1, characterized in that the imaginary part of the complex impedance is constituted by a capacity so as to make the detector means responsive to a breakdown of said conductor elements.

3. A pipe system according to claim 1, comprising a number of pipe length sections each having individual detector means in the form of a tone generator, these generators working on individual frequencies and all having their output connected to a central surveyance station, each generator being connected with the conductor elements along the particular pipe length section in such a manner that the output signal of the generator ceases when the conductivity between the conductor elements exceeds a predetermined value, characterized in that the output of the phase comparator belonging to each pipe length section is connected to an electronic switch adapted to cause ceasing of the generator output, preferably by cutting ofi the voltage supply to the generator, in response to said phase difference changing beyond a value corresponding to said predetermined value of the conductivity.

4. A pipe system according to claim 1, characterized in that the detector unit is adapted so as to be deactuated into its normal condition in response to the phase difference returning towards its normal value through a value corresponding to a conductivity in the hygroscopic material which is lower than the conductivity at which the detector unit is actuated.

5. A pipe system according to claim 1, characterized in that said alternate voltage source includes an oscillator having outputs connected respectively to one of said conductor elements and to an input of said phase comparator.

6. An insulated pipe system comprising: at least first and second conductor pipes, each of said first and second conductor pipes being surrounded by a normally dry and electrically non-conducting, hydroscopic material;

a plurality of elongated, electric conductor elements embedded in said material, a first of said plurality of conductor elements of said first conductor pipe being connected to an electric power source, and a first of said plurality of conductor elements of said second conductor pipe being connected to a central station, the other of said plurality of conductor elements of each of said first and second conductor pipes being interconnected to form a complex impedance with the real part of said complex impedance being constituted by the resistance of said conductor elements;

an alternate voltage source having an output coupled to said interconnected plurality of conductor elements;

phase comparison means having a first input connected to said output of said alternate voltage source and a second input coupled to said interconnected plurality of conductor elements to receive a signal representing the phase of said complex impedance for comparing the phase of the output signal of said alternate voltage source with said phase of said complex impedance; and

detector means connected to the output of said phase comparison means for providing an output signal to said central station representative of a phase difference changing beyond a predetermined value.

7. A pipe system according to claim 6, wherein said first and second conductor pipes are arranged approximately in parallel with said first conductor pipe being a flow pipe in a subterranean heating system, and said second conductor pipe being a return pipe in said heating system.

8. A pipe system according to claim 6, wherein said interconnected plurality of conductor elements are inductively coupled to said output of said alternate voltage source and to said second input of said phase comparison means by a transformer.

9. A pipe system according to claim 6, wherein said detector means includes a single frequency generator coupled to said central station and switch means connected to said phase comparison means for controlling said single frequency generator.

10. A pipe system according to claim 9, wherein said single frequency generator is inductively coupled by a transformer to said first conductor element of said second pipe connected to said central station. 

1. An insulated pipe system such as a subterranean district heating pipe system comprising a conductor pipe surrounded by a normally dry and electrically non-conducting, but hygroscopic material in which there is enclosed elongated electric conductor elements connected to means for detecting the occurrence of an electric conductivity in the hygroscopic material due to intrusion of moisture therein, characterized in that the conductor elements between which the conductivity should be detected are connected to an alternate voltage source and are mutually connected so as to form a complex impedance, the real part of which is constituted by the resistance between the conductor elements through the hygroscopic material, the detecting means comprising a phase comparator connected so as to compare the phase of the output signal from the alternate voltage source with the phase of the signal through the complex impedance and to actuate a detector unit in response to the phase difference between the compared signals changing beyond a predetermined value.
 2. A pipe system according to claim 1, characterized in that the imaginary part of the complex impedance is constituted by a capacity so as to make the detector means responsive to a breakdown of said conductor elements.
 3. A pipe system according to claim 1, comprising a number of pipe length sections each having individual detector means in the form of a tone generator, these generators working on individual frequencies and all having their output connected to a central surveyance station, each generator being connected with the conductor elements along the particular pipe length section in such a manner that the output signal of the generator ceases when the conductivity between the conductor elements exceeds a predetermined value, characterized in that the output of the phase comparator belonging to each pipe length section is connected to an electronic switch adapted to cause ceasing of the generator output, preferably by cutting off the voltage supply to the generator, in response to said phase difference changing beyond a value corresponding to said predetermined value of the conductivity.
 4. A pipe system according to claim 1, characterized in that the detector unit is adapted so as to be de-actuated into its normal condition in response to the phase difference returning towards its normal value through a value corresponding to a conductivity in the hygroscopic material which is lower than the conductivity at which the detector unit is actuated.
 5. A pipe system according to claim 1, characterized in that said alternate voltage source includes an oscillator having outputs connected respectively to one of said conductor elements and to an input of said phase comparator.
 6. An insulated pipe system comprising: at least first and second conductor pipes, each of said first and second conductor pipes being surrounded by a normally dry and electrically non-conducting, hydroscopic material; a plurality of elongated, electric conductor elements embedded in said material, a first of said plurality of conductor elements of said first conductor pipe being connected to an electric power source, and a first of said plurality of conductor elements of said second conductor pipe being connected to a central station, the other of said plurality of conductor elements of each of said first and second conductor pipes being interconnected to form a complex impedance with the real part of said complex impedance being constituted by the resistance of said conductor elements; an alternate voltage source having an output coupled to said interconnected plurality of conductor elements; phase comparison means having a first input connected to said output of said alternate voltage source and a second input coupled to said interconnected plurality of conductor elements to receive a signal representing the phase of said complex impedance for comparing the phase of the output signal of said alternate voltage source with said phase of said complex impedance; and detector means connected to the output of said phase comparison means for providing an output signal to said central station representative of a phase difference changing beyond a predetermined value.
 7. A pipe system according to claim 6, wherein said first and second conductor pipes are arranged approximately in parallel with said first conductor pipe being a flow pipe in a subterranean heating system, and said second conductor pipe being a return pipe in said heating system.
 8. A pipe system according to claim 6, wherein said interconnected plurality of conductor elements are inductively coupled to said output of said alternate voltage source and to said second input of said phase comparison means by a transformer.
 9. A pipe system according to claim 6, wherein said detector means includes a single frequency generator coupled to said central station and switch means connected to said phase comparison means for controlling said single frequency generator.
 10. A pipe system according to claim 9, wherein said single frequency generator is inductively coupled by a transformer to said first conductor element of said second pipe connected to said central station. 